Several new prostate-cancer tests aim to reduce needless biopsies and unnecessary treatments by sorting out harmless from aggressive tumors

When Al Piazza learned he had prostate cancer, his first thought was, “Let’s get this out and be done with it,” he says. But his urologist, Jeremy Lieb, said the side effects of treatment could be more harmful than the cancer itself.

Dr. Lieb ran a genetic test on the patient’s biopsy sample, which calculated that Mr. Piazza, then 70 years old, had only a 3% chance of dying from prostate cancer over the next 10 years if he left the tumor untreated.